1. Field of the Invention
The present invention relates to an optical element driving apparatus operable to move an optical element such as a lens, and particularly to an optical element driving apparatus using a voice coil motor as a driving source and a magnetic sensor for detecting a position of the optical element.
2. Description of the Related Art
Optical element driving apparatuses are provided in lens barrels of optical apparatuses such as video cameras and digital still cameras to move a lens in an optical axis direction for zooming or focusing, or to move a lens in a direction orthogonal to the optical axis direction for reducing image blur caused by hand jiggling.
In such optical element driving apparatuses, disposing a magnetic sensor as a position detector close to a voice coil motor as a driving source causes output of the magnetic sensor to be influenced by magnetism (magnetic flux) leaking from the voice coil motor, which deteriorates position detection accuracy of the optical element.
A voice coil motor used in an optical element driving apparatus disclosed in Japanese Patent Laid-Open No. 2011-75674 includes a first yoke extending in an optical axis direction and a second yoke disposed orthogonally to the optical axis direction. The voice coil motor has, in order to suppress magnetic flux leakage, a smaller thickness of the second yoke than that of the first yoke and a wider width of the second yoke than that of the first yoke to make cross-sectional areas (thickness×width) of the first and second yokes equal to each other.
Moreover, a voice coil motor used in an optical element driving apparatus disclosed in Japanese Patent Laid-Open No. 2000-241694 includes a yoke provided with a protrusion or a through hole formed at a position shifted from a center of a magnet attached to the yoke. The protrusion or the through hole formed at the position shifted from the center of the magnet shifts a magnetic center, which reduces influence of magnetic flux leakage on a magnetic sensor.
The voice coil motor disclosed in Japanese Patent Laid-Open No. 2011-75674 can suppress magnetic flux leakage from a joint portion of the first yoke with the second yoke, which is an end portion in the optical axis direction of the first yoke, but cannot sufficiently suppress magnetic flux leakage from a lateral opening of the first yoke.
On the other hand, the protrusion or the through hole formed in the yoke of the voice coil motor disclosed in Japanese Patent Laid-Open No. 2000-241694 provides a small effect of suppressing the magnetic flux leakage, which makes it difficult to sufficiently reduce the influence of the magnetic flux leakage on the magnetic sensor.